COLUMBUS – A federal judge has extended a months-long moratorium on executions in Ohio into next year as questions mount about the effectiveness of a new, two-drug combination being used to carry out the death penalty.

The ruling by federal judge Gregory Frost will delay executions scheduled for September, October and November and highlights the ongoing problem faced by states in obtaining drugs to put inmates to death.

The last moratorium was scheduled to expire this week.

The one-page order that Frost issued Friday extends it through Jan. 15. It affects the state's latest death penalty policy change, which was announced in late April and increases the amount of the sedative and painkiller Ohio uses.

Ohio's first choice for a drug is compounded pentobarbital, a specialty version of the drug it used previously with few problems. But it has been unable to obtain supplies of that drug and so switched to its backup method of the sedative midazolam and the painkiller hydromorphone.

On Jan. 16, an Ohio inmate repeatedly gasped during the record 26 minutes it took him to die.

On April 29 in Oklahoma, Clayton Lockett died of an apparent heart attack 43 minutes after his execution began with a three-drug method that starts with midazolam. Officials pointed to improper insertion of the needle delivering the drugs.

On July 23, an inmate took nearly two hours to die in Arizona, which also uses midazolam and hydromorphone.

Missouri and Texas both have supplies of compounded pentobarbital, though the states won't reveal their sources, and have used them to carry out several executions successfully in recent months.

The two states are scheduled to carry out the country's next executions, both on Sept. 10. In Missouri, Earl Ringo is set to die for a July 4, 1998, double slaying at a Ruby Tuesday restaurant in Columbia, where he was a former employee. In Texas, Willie Trottie is scheduled to die from a single dose of compounded pentobarbital for shooting his former girlfriend and her brother in Houston in 1993.

For decades, states used the same three-drug formula for lethal injections: a sedative that rendered the inmate unconscious, usually sodium thiopental, followed by a paralytic agent, usually pancuronium bromide, and finally the drug that stopped the heart, potassium chloride.

But in recent years, major drugmakers, many of them in Europe, stopped selling pharmaceuticals for use in executions, citing ethical concerns. By 2011, with sodium thiopental no longer available, Ohio became the first state to use pentobarbital in a single-drug execution.

Allen Bohnert, the lead defense attorney challenging the use of the two-drug method, declined to comment.

The state prisons agency said it "remains committed to carrying out executions in a humane and lawful manner," according to spokeswoman JoEllen Smith.

The next execution scheduled in Ohio was to have occurred Sept. 18, when Ronald Phillips was set to die for the 1993 rape and death of his girlfriend's 3-year-old daughter in Akron.